For suppliers of LNG cargo transfer systems, achieving a safety integrity level 2 (SIL2) rating is a key step in building customer confidence
Safety management systems that reduce and monitor risk help operating companies meet their legal obligations to ensure safety in the workplace. Under such systems a safety case, justifying the risk management position, must be completed for inspection by the regulatory authorities.
One of the most safety-critical features of gas carrier operations is the emergency shutdown (ESD) of the cargo transfer process. Among the basic requirements for the vessel’s ESD system – as laid down in the International Code for the Construction and Equipment of Ships carrying Liquefied Gases in Bulk (IGC Code) – is the provision that the system be initiated by manual trips or thermal devices. However, operating conditions at most liquefied gas ship/shore interfaces mean these core initiators need to be supplemented with other techniques.
Linking ship and shore ESD
The IGC Code has no jurisdiction over the activation of a shore installation’s ESD system. However, it does require that ship and shore agree cargo transfer procedures and adjust loading rates to limit the surge pressures generated when valves close in an emergency. Invariably, gas ship and shore ESD systems are linked, so that the activation of a shutdown trip on the ship will send an ESD signal to shore, and vice versa.
In recent years, the industry has begun to place greater emphasis on the quality and performance of critical safety systems over their entire lifecycle. A safety-instrumented system (SIS) must be capable of providing the level of improvement claimed in the safety case.
Conformity with either of two International Electrotechnical Commission (IEC) standards – IEC 61508 or IEC 61511 – is accepted as an effective way of demonstrating that the safety-instrumented protection measures can provide the claimed reduction in risk.
IEC 61508 is a generic standard for functional safety using electronic and programmable electronic equipment, while IEC 61511 is the standard for functional safety systems within the process industry sector.
The standards cover all stages of an equipment application project, from initial concepts and hazard studies through to operation, maintenance and modification. Provisions dealing with SIS design are laid down, as are those for safety integrity level (SIL) analysis.
SIL ratings are a measure of a safety system’s performance; the SIL2 rating is of particular relevance to gas carrier ESD systems and emergency release couplings. SIL2 is a globally recognised standard which requires an extensive testing and assessment programme to demonstrate the safety, integrity and reliability of the technology in question.
"The industry has begun to place greater emphasis on the quality and performance of critical safety systems over their entire lifecycle"
SIL2 in practice
Leading suppliers of LNG coupling systems have introduced steps to demonstrate that their equipment conforms to SIL2 safety requirements. Attainment of the relevant certification provides customers with an additional measure of confidence in the long-term performance capabilities of the equipment in question.
KLAW LNG has had an LNG safety integrated level safety instrumented system (SILSIS) in operation in Jamaica for two years. The company claims it is the world’s first SIL2-compliant automated system specifically designed for managing LNG transfers and emergency situations in flexible hose operations.
The system has been in place at the Micro LNG terminal in Jamaica’s Montego Bay since October 2016. The initial SILSIS ship-to-shore flexible hose transfers involved the discharge of LNG cargo from the 6,500-m3 Coral Anthelia to the shoreside cylindrical pressure vessel storage tanks utilised by the JPS Bogue power station.
SILSIS provides continuing system diagnostics, both before and during LNG transfers, while monitoring operations and offering complete control over ESD1 and ESD2 procedures and providing black-box records of transfer data. It also ensures the LNG transfer operation is always maintained at SIL2, is highly ‘available’ and in a ‘ready for transfer’ condition.
ESD1 and ESD2 represent the two-stage sequence in an emergency shutdown scenario. In the ESD1 part of the procedure, the cargo transfer operation is stopped in a quick and controlled manner, while in the rapid follow-up ESD2 phase the emergency release system is activated.
KLAW LNG’s Julian Fairman explained “To be SIL2-compliant, operations and procedures must also maintain SIL2 compliance over the operational life of the system. SILSIS is a fully-automated, programme logic-controlled system and removes many human elements from the transfer process. This maximises cost-efficient availability.
“SILSIS offers minimal operational disruption by being able to proof test and diagnose issues without the need for invasive inspection. In addition, its easy-to-use, real-time interface ensures that operators can follow systematic procedures without the risk of distraction.”
More SIL2 certifications
In recent months Alpha Process Controls (APC) has achieved a SIL2 certification for its marine emergency release coupling (ERC). APC’s SIL2 rating confirms the coupling’s consistent ability to prevent loss of product during the transfer of hazardous materials, including LNG. APC’s coupling systems are deployed across ship-to-ship, ship-to-shore and bunkering applications.
The company’s marine ERC employs a mechanical, rather than hydraulic, release activation and features a two-stage ESD1 and ESD2 operation that enables the controlled shutdown of internal valves and the coupling separation. The ERC coupling can be operated mechanically, or through a remote operator-activated switch.
APC’s ERC can be specified with a pre-ESD1 alarm, which detects ship separation, and can be linked to the ship’s ESD1 shutdown process. This safety feature complements the ERC’s innovative, in-built damping system to reduce the effects of pressure spikes should the coupling be called upon to separate during full-flow transfer. This would typically occur in the case of a vessel drifting off during LNG transfer.
Available in sizes from 4-to-10 inches in diameter, APC’s marine ERC has secured class-society approval. It also meets the requirements of BS EN 1474-1 (2008), Installation and equipment for liquefied natural gas - Design and testing of marine transfer systems. The company reports that certification to this recognised industry standard further demonstrates the efficacy of the system.
The SIL2 assessment and certification of APC’s marine ERC was undertaken by UK consultancy Technis, led by Dr David J Smith. Dr Smith chairs the Chartered Institution of Gas Engineers and Managers (IGEM) panel, which develops guidelines on safety-related systems and was a founder member of the Safety Critical Systems Committee of the Institution of Electrical Engineers (now IET).
MannTek’s lightweight LNG transfer system is utilised by Coralius as it fuels the LNG-powered tanker Fure West
In September 2017 the Swedish coupling manufacturer MannTek introduced a small-scale LNG transfer system that it claimed was up to 50% lighter than other such systems then available on the market. Developed with LNG bunkering as a particular target market, the weight-saving package was designed to make it safer and easier for operators to manually lift and manoeuvre the connection.
The lightweight transfer system consists of MannTek’s dry cryogenic couplings (DCCs), cryogenic breakaway couplings, LNG hoses, an ESD system and a high-pressure nitrogen system. Following successful completion of a factory acceptance test, the system was first deployed on Coralius, the 5,800-m3 Baltic and North Sea LNG bunker vessel, jointly owned by Sirius Shipping and Anthony Veder.
MannTek said its new transfer system complies with the relevant standards set by international associations, institutes and regulatory bodies and has class approval from DNV GL, BV and Lloyd's Register. The package can also be provided with a SIL2 certification.
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